Lambda controls were first configured as two-step controls since the lambda probe utilized therein has an sharp non-linear step response approximately about the lambda value one. However, in recent years, probes have been developed to the point where they can be utilized and have a relatively constant measurement accuracy for the lambda value in a larger range about the value one. In this way, it has become possible to control even so-called lean engines or to undertake the control of engines with rich operation such as during warm-up or at full load.
A further advantage of continuous lambda control is that notwithstanding the relatively large dead time, they can be provided in a lambda control circuit with a D-component (derivative component). This enables such controls to react very rapidly to changes of the lambda value as they occur during transient operation of the controlled engine. Notwithstanding the rapid response, the continuous control can always control with low control oscillations even when used in different lambda value ranges. According to the state of the art, this is viewed as being a primary objective of lambda control methods.
The methods of continuous lambda control developed up to the present have led to a further reduction of toxic material in the exhaust gas of an engine having a catalyzer. The efforts for still further reduction however continue undiminished.